1. Field of the Invention
The present invention relates generally to solar cells, and, in particular, to a method, apparatus, and article of manufacture of a reduced band gap absorber for solar cells.
2. Description of the Related Art
Solar energy created through the photovoltaic effect is the main source of power for most commercial and government spacecraft. The amount of power generated by an array of solar cells is limited by the launch volume and launch weight. These restrictions limit the capability of the spacecraft. Similarly, any terrestrial solar cells are limited by the size of an array that can be installed in a given installation.
To be able to increase payload capability, or power delivery capability, the power per unit area for the solar cell array must be increased. Increasing the efficiency of the solar cell is of primary importance for enabling near-earth missions. The dominant solar cell technology for this application is a combination of subcells comprising Gallium Indium Phosphide (GaInP), Gallium Arsenide (GaAs), and Germanium (Ge), which is typically called a triple-junction, or “3J”, device.
The current best efficiency of a 3J device at the Beginning Of Life (BOL) is 28.6%, which degrades over time to an End Of Life (EOL) final percentage. Solar cells used in space must survive for up to fifteen years in an environment rich in atomic oxygen and energetic sub-atomic particles, which degrades the solar cells significantly. The general objective of any change in the design of solar cells is to reduce the cost of the device, the BOL efficiency, or to decrease the rate of degradation such that the EOL efficiency is higher as well.
Several approaches have been used to try to make solar cells more efficient or less costly. One approach is to use a multiple quantum-well (MQW) approach, which makes the efficiency go up but also makes the cells much more expensive because of the tolerances required to make an MQW structure. Other approaches use layer thickening, additional subcell structures, or mismatch of the subcell materials, each of which adds to the cost as well as the weight of the cell, limiting the usefulness of such approaches.
It can be seen, then, that there is a need in the art for more efficient solar cells.